In an optical communications system, an optical switch performs an O-E-O (optical-electrical-optical) conversion where an optical signal is converted into an electrical signal to be switched at an electrical level and then is reconverted into another optical signal. However, the O-E-O conversion is a very complicated process since it requires 3R (retiming, reshaping and regeneration) of the signal. Further, since employed in this O-E-O switching mechanism is a WDM (wavelength division multiplexing) technique whereby a plurality of lights having different wave lengths are transmitted through only one optical fiber port, a transmission velocity is limited to a very small range.
A switching device plays an important role in a modern communications system, and one among the most important techniques required in such a switching device is a switching technique that determines a maximum capacity of a switching system. It is expected that every subscriber will use a bandwidth ranging from several hundreds of Mbps to several tens of Gbps in a next generation communications network. In order to increase the switching capacity, two methods may be employed: one is to increase a speed of the conventional electrical switch and the other is to use a new component, i.e., an optical switch. However, the former has many defects. For example, a time delay cannot be avoided since the electrical switch involves two conversion processes in which an optical signal is first converted into an electrical signal and, then, the electrical signal is reconverted into another optical signal to be transmitted through a selected transmission channel. Furthermore, since the electrical switch has a very complicated structure, manufacturing costs are increased. In the meanwhile, in order to obtain competitiveness in terms of price, the switching device is required to be further scaled down. Thus, considering the above-described drawbacks of the electrical switch and the recent trend for the more miniaturized switching device, attentions are directed to an optical switch that is capable of obtaining high capacity and competitiveness in price without involving an O-E-O conversion.
For this reason, a switching technique using a micro mirror controlled by using a MEMS (micro electro-mechanical systems) type actuator is gaining popularity in recent years. This type of optical switch using the micro-mirror can accommodate more than 256 ports therein and, thus, is expected to be widely utilized in developing an optical module for use in an OXC (optical cross connect) system.
As mentioned above, the optical switch is implemented by using the MEMS. The MEMS refers to a 3-D microstructure fabrication technique branched from a semiconductor processing technology. To be more specific, the MEMS is employed to fabricate macroscopic mechanical elements to have a micron or nano size. By using the MEMS technique, not only a simple mechanical structure but also a variety of intelligent micro systems can be fabricated by integrating a micro sensor, an actuator, etc., with a logic circuit. Accordingly, the MEMS has a wide range of applications: communications systems, a military industry, a medical instrument manufacturing, aeronautical engineering, etc. Particularly, the optical switch is given a great attention in the field of optical communication since it is expected to be fabricated by using the MEMS technology to be available in the near further.
Optical switches known so far are technically classified into two types according to their optical channel switching methods: one is a type using a micro mirror and the other is a type using a refraction index of a micro fluid.
The optical switch using the micro mirror is divided into a 2D planar switch having a two-dimensional array and a 3D free-spatial switch having a three-dimensional array. Though the 2D switch has many advantages in that it allows optical fibers to be readily arranged and has a simple structure due to its employment of an on-off operation type mirror, the 2D switch cannot be fabricated to accommodate therein 32×32 or more ports. Thus, the 3D switch that shows a greater expandability is more adequate for use in a backbone network requiring Tbps level capacity.
In general, actuators used in the micro device such as the above-described optical switch has been fabricated by using electrostatic force. However, the actuator using electrostatic has disadvantage in that it accompanies an increase of a driving voltage, e.g., more than 200V, and it has non-linear characteristics. Also, it is not preferable since a pull-in phenomenon of a micro mirror being adhered to a substrate occurs. Furthermore, it is difficult to obtain a large displacement angle of the mirror and precisely control an optical channel by revolving the micro mirror with respect to two axes, e.g., a X and a Y axis.